It has to do with horsepower.
Q: Why do cars have two headlights?
A: The obvious answer: There’s more illumination in two headlights than one. But then why not use three headlights? Or 30? I’ll now prove I can write 500 words on anything.
At first, driving at night was itself a ludicrous idea. The 1896 Duryea, America’s first production car, didn’t have lights at all. But headlights weren’t unknown—horse-drawn carriage were sometimes equipped with acetylene lamps. But the light has to cast a beam around those large animals. So, horsemen hung one lamp on either side of the carriage, each lighting down the side of the horse, or horses. That made sense.
Some brass-era cars tucked their engines under the driver’s seat or out behind the rear axle. The light (or lights) could have been positioned anywhere. But most early carmakers stuck with the traditional carriage arrangement. Then as car design more or less standardized around a front-mounted, water-cooled engine, having a headlight on either side of that the engine and its radiator was the only logical placement—not all that dissimilar from setting on either side of a horse’s rump.
But single headlamps were occasionally used on cars. In 1936 the brilliant French engineer Pierre-Jules Boulanger, obsessed with weight reduction and simplicity, designed the original Citroen 2CV around a single headlight since that’s all that was required by French law. By the time that car was in regular series production it had two headlights.
Are there other reasons? Sure. With two headlights, if you bust one you can still drive home on the other. Even in a Deux Chevaux.
While developing the original Volkswagen Type 1 Beetle in the 1930s, Ferdinand Porsche experimented with headlight placement, but ultimately the conventional position outboard in the fenders allowed for the largest front trunk opening.
The smallest production car ever, the 1962 Peel P50, used a single headlamp because, it seems, at 41-inches across it wasn’t wide enough for two. During the 1950s, illustrators Stan Mott and Robert Cumberford jokingly drew up the absurd Cyclops single-headlight microcar for Road & Track magazine.
Preston Tucker used three headlights for his Tucker 48 in 1948. Developed as a safety car, the Tucker’s engine was in back so a third center-mounted headlight could be mounted in the nose. Moving with the front wheels, the center lamp would supposed to light up around corners. The Czech maker Tatra, used third headlights too. But those center lights were also vulnerable to damage.
The 1986 Mercury Sable and 1988 Pontiac Grand Prix sedan had headlights in the traditional positions, but added a backlit plastic panel between them. Those center panels were more about decoration than illumination. And they weren’t cheap to fix after a collision.
In off-road and rally racing, the vehicles are equipped with numerous high-powered lights. But lights aren’t free and production cars are built to a price.
The National Highway Traffic Safety Administration regulates headlights under Section 108 in its Code of Federal Regulations. Section 5.1.1 reads “Except as provided in succeeding paragraphs of this S5.1.1, each vehicle shall be equipped with at least the number of lamps, reflective devices, and associated equipment specified in Tables I and III and S7, as applicable.” And the cheapest way to meet that regulation is to use two headlights. Two works.
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